Cross resistance, inheritance and fitness advantage of cyetpyrafen resistance in two-spotted spider mite, Tetranychus urticae.

Cyetpyrafen belonging to mitochondrial electron transport inhibitors of complex II (METI II) has been widely applied to manage pest mites in China. To investigate the adaption of Tetranychus urticae in the evolution of cyetpyrafen resistance, a study of cross resistance, mode of inheritance and fitness comparison of resistance using indoor cyetpyrafen resistant strain (resistance ratio, RR > 2, 000-fold) was executed. Cyet-R showed serious cross resistance to cyenopyrafen (>2500-fold) and cyflumetofen (~190-fold). The number of resistant genes was evaluated via chi-square (χ2) test and the concentration-response curve regarding goodness-of-fit between observed and the expected mortality. The LC50s of F1RS (Cyet-R♀ × Tu-YN♂) and F1SR (Tu-YN♀ × Cyet-R♂) were 3126.30 mg/L and 2743.97 mg/L, respectively, without significance, suggesting autosomal inheritance. The degree of dominance (D) values of F1RS and F1SR ranged between 0 and 1, revealing an incompletely dominant inheritance in the tested population of Tetranychus urticae. Plots of concentration-response data for the orthogonal backcross and reverse backcross progenies showed a significant deviation from the expected lines, pointing out a polygenic inheritance. Besides, lifetable analysis showed a fitness advantage of Cyet-R with a significantly decreased adult preadult period and significantly increased total fecundity. This study suggested that cyetpyrafen resistance against T. urticae was inherited as autosomal, incompletely dominant and multigenetic and characterized with serious cross resistance and fitness advantage. Therefore, rational application and preventive strategy should be considered to sustain the efficacy of cyetpyrafen against T. urticae.

Fabrication and Characterization of Viton@FOX-7@Al Spherical Composite with Improved Thermal Decomposition Property and Safety Performance.

To achieve a uniform distribution of the components and a better performance of aluminized composite explosives, Viton (dipolymers of hexafluoropropylene and vinylidene fluoride) @ FOX-7 (1,1-diamino-2,2-dinitroethylene) @Al microspheres and FOX-7/Viton@Al were synthesized by spray-drying strategy contrastively. Viton@FOX-7@Al owned porous and loose morphology and good sphericity with a retained crystal phase of FOX-7 and aluminum. The 23.56% fluorine content on Viton@FOX-7@Al surface indicated that Viton was completely coated on the surface of the particles. Nanosized aluminum (nAl) in Viton@FOX-7@Al had a certain catalytic activity on the thermal decomposition process of FOX-7 resulting in a depressed exothermic peak temperature and reduced apparent activation energy relative to nAl in FOX-7/Viton@Al. Because of the specific structure and the synergies between each individual component, Viton@FOX-7@Al showed reduced impact sensitivity and friction sensitivity than those of FOX-7/Viton@Al. In brief, Viton@FOX-7@Al with multilevel coating structure possessed comparatively low thermal decomposition energy requirement and improved safety performance.

Transgenic cotton expressing CYP392A4 double-stranded RNA decreases the reproductive ability of Tetranychus cinnabarinus.

As a polyphagous pest, Tetranychus cinnabarinus has the ability to overcome the defense of various hosts, and causes severe losses to various economically important crops. Since the interaction between pest and host plants is a valuable clue to investigate potential ways for pest management, we intend to identify the key genes of T. cinnabarinus for its adaption on cotton, then, with RNA interference (RNAi) and transgenic technology, construct a transgenic cotton strain to interfere with this process, and evaluate the effect of this method on the management of the mites. The difference of gene expression of T. cinnabarinus was analyzed when it was transferred to a new host (from cowpea to cotton) through high-throughput sequencing, and a number of differentially expressed genes involved in detoxification, digestion and specific processes during the development were classified. From them, a P450 gene CYP392A4 with high abundance and prominent over-expression on the cotton was selected as a candidate. With transgenic technology, cotton plants expressing double-stranded RNA of CYP392A4 were constructed. Feeding experiments showed that it can decrease the expression of the target gene, result in the reduction of reproductive ability of the mites, and the population of T. cinnabarinus showed an apparent fitness cost on the transgenic cotton. These results provide a new approach to restrict the development of mite population on the host. It is also a useful attempt to control piercing sucking pests through RNAi and transgenic technology.

Expression characteristics of two novel cytochrome P450 genes involved in fenpropathrin resistance in Tetranychus cinnabarinus (Boisduval).

The carmine spider mite, Tetranychus cinnabarinus, which is also considered as the red form of Tetranychus urticae, is one of the most serious mite pests on crops. It is capable of rapidly developing resistance to acaricides, and has caused difficulty in controlling. However, the resistance mechanism of this mite remains unclear at molecular level. As a member of main detoxification enzymes, cytochrome P450 monooxygenases (CYPs or P450s) play important roles in the development of acaricide resistance in arthropods. In this study, two novel P450 genes (CYP389B1 and CYP392A26) were identified and characterized from T. cinnabarinus. The opening reading frames (ORFs) of CYP389B1 and CYP392A26 contained 1545 and 1488 nucleotides, which encode 514 and 495 amino acids, respectively. Phylogenetic analysis showed that CYP389B1 and CYP392A26 were most closely related to CYP389B1 and CYP392A4 from T. urticae, respectively. When treated with piperonyl butoxide (PBO), an inhibitor of P450s, the resistance ratio of fenpropathrin-resistant (FeR) strain decreased from 101- to 75-fold, which suggested a correlation between P450 and fenpropathrin-resistance in T. cinnabarinus. Furthermore, constitutive over-expressions of CYP389B1 and CYP392A26 were detected in FeR strain. Meanwhile, the expressions of CYP389B1 and CYP392A26 were inducible in FeR strain after treatment in 6, 12 and 24 h with LC30 of fenpropathrin; especially, the expression of CYP392A26 increased to a markedly high level (20.88-fold higher than in the control) after treatment in 6 h. However, there was no significant difference between treatment and control in susceptible strain. Furthermore, stage specific expression profiles of these two genes did not show significant difference among developing stages, except for eggs, in which the mRNA levels were quite low. The results indicate that CYP389B1 and CYP392A26 were involved in the fenpropathrin-resistance in T. cinnabarinus, and the expression of CYP392A26 was more sensitive to fenpropathrin stress. These findings provide clues for further elucidating the function and regulation mechanism of these two cytochrome P450 genes in T. cinnabarinus.